text:
Do pilots have to stop at the hold position of the takeoff runway?
Or in other words, is the takeoff clearance ever given (implicitly or explicitly) before the aircraft reaches the hold position, so that the pilot can keep rolling through the hold line and to the takeoff roll?

Related

Ah ok thanks for the tip...makes sense...new to this.

No, there is no mandatory stop. Typical clearances given before departure are:

BigAir 123, hold short of runway 36.
BigAir 123, line up and wait runway 36.

Former phraseology in the US was "position and hold".

BigAir 123, behind landing A320, line up and wait runway 36, behind.

Note the word "behind" being repeated at the end of the clearance.
The interesting ones:

BigAir 123, are you ready for immediate departure?

It will be asked by the tower controller to assess if they can squeeze BigAir 123's departure between two landings, for example.

BigAir 123, cleared for takeoff runway 36.

It can be given to an aircraft still on the taxiway. In such case, BigAir 123, who will have proceeded through checklists and briefings while taxiing, will turn into the runway and takeoff, without having to stop at any point.
It is possible that the crew actually needs to stop, to finish their preparations. In such case, they will normally report not ready for departure, if asked. The tower controller doesn't want aircraft making unexpected stops on the runway, especially in a single-runway airport, this can result in the following landing having to go-around.
Also note that the word "takeoff" is used only in the context of an actual takeoff clearance or its cancellation. Otherwise the word "departure" is used, e.g., are you ready for departure? Also see the Tenerife disaster.

No, it is not always mandatory to stop at the hold line. Yes, the Tower controller can give you clearance to enter the runway (cross the hold line) before you actually stop at the hold line, in which case you're not required to stop there.
If the controller gives an aircraft the clearance:

Runway XX, Clear for Takeoff

Then the aircraft may both cross the hold line to enter runway XX and proceed to take off on it. Whether the aircraft stops after lining up at the end of the runway is up to the discretion of the Captain. Some pilots will chose to come to a stop after lining up and then select takeoff power, while others will just keep rolling and select takeoff power once they're aligned with the runway.
The controller may also add "No Delay" to the clearance. In that case, the pilot should not stop if it can be avoided or should at least keep the stop to an absolute minimum. If the pilots are unable to do that, they should reject the clearance and not enter the runway.

If the controller gives an aircraft the clearance:

Runway XX, Line Up and Wait

Then the aircraft is clear to cross the hold line to enter runway XX, but, after lining up, should stop and wait for takeoff clearance before proceeding to initiate the takeoff run.

Either of these clearances can be given while the aircraft is still rolling on the taxiway and, in either case, the aircraft may cross the runway hold line to enter the runway without stopping.

So the answer should be "No", not "Yes"?

@Dubu Hmm... Regarding the title question, you're correct. Unfortunately, the title question and the body of the question are actually opposites of each other. The 'Yes' in this answer is meant to address the question in the body, rather than the title. I'll edit to make this a bit more clear.

Two main instructions give a pilot clearance to cross a hold line: instructions to cross, and instructions for takeoff/line up. Neither clearance requires the aircraft to actually stop at the hold line. If the tower controller feels that clearance can be given early, they may do that. This is particularly true if a runway is not active and would have no conflicts for crossing aircraft, or if there is no other traffic for the runway at the time.

There's a third pretty common clearance to cross a hold short line: line up and wait.

@nexus_2006 good point, added.

While the above answers are technically correct--you can be given takeoff clearance while taxiing--this is rare.
The standard sequence is to receive a taxi clearance to the runway, where it is then mandatory to stop before the hold line.  Once there, you get your takeoff clearance, allowing you to enter the runway.
You COULD request takeoff clearance as you are approaching the runway, obviating the need to come to a stop, but a towered airport is usually busy enough that the controller will want to see you at the line, ready to go, before giving you the runway.
Disclaimer: this comes from the perspective of a piston-airplane pilot.  Because we have to do a run-up before takeoff, it is particularly true that we won't get clearance until we are ready at the line.  A jet, which does not have this requirement, might get an earlier clearance.

Yes, as this question discusses, at least in the U.S., it's different for turbine-powered aircraft. According to the AIM, "The tower controller will consider that pilots of turbine-powered aircraft are ready for takeoff when they reach the runway or warm-up block unless advised otherwise."

I'd just like to suggest that you avoid references like "the above answers" on Stack Exchange sites. The order of the answers can change due to voting or the order selection (active, newest, or votes), so it can be unclear which answers you're referring to.

Southwest 3828, Midway tower, runway 31C,  line up and wait, don't plan on stopping.

That's in the audio but not in the subtitles, listen for it at 0:59.
ATC has a lot in motion, with Delta lining up on the cross runway and a short final approaching the other cross runway, and IIRC another flight on a 10-mile final on Southwest's runway.  Southwest has gotta go pretty much right now or he'll lose the window of opportunity, and so ATC is clearing him past every stop point before he can reach it.
ATC also cleared Delta to roll past the hold-short line, but did not clear him to takeoff.  If Delta had been paying more attention to chatter, he'd have the situational awareness to know what was going on.

Over in the railroad world, throwing clearances ahead of the train is SOP because of the high cost of restarting a train.  I once saw a beautifully written train order that is the old-school version of this same thing, giving statutory wait instructions you won't be using:
   Extra 4419 East [a lowly switch job] move Echo to Alpha, take siding for Train 1.
   Train 1 [the late Presidential Limited] hold mainline and wait at
       Alpha        until 7:00pm
       Bravo        until 7:10pm
       Charley      until 7:20pm
       Delta        until 7:30pm
         for Extra 4419 East.

This schedule is impossible for Train 1, it can't get there at those times so it won't wait.  The order is for the benefit of X4419, who can now choose its meeting point with #1, without any further communication needed.


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What are the regulatory requirements requiring Weight and Balance be onboard aircraft for flight?
The common mnemonic ARROW teaches private pilots a Weight and Balance must be onboard the aircraft for flight (usually included in the POH/AFM). What is the regulatory requirement for this?
In my research I've found a couple possible reasons but none current and regulatory.

"W&B must be in the AFM as per 14 CFR 23.1583"

This regulation appears to be part of the 14 CFR 23 rewrite as it's no longer listed under part 23.
14 CFR 23.2620 states The Airplane Flight Manual must contain the following information (1) Airplane operating limitations;(2) Airplane operating procedures;(3) Performance information;(4) Loading information; and(5) Other information that is necessary for safe operation because of design, operating, or handling characteristics.

"W&B must be onboard if required by the TCDS"

This may be both true and regulatory but in my case the TCDS only states the W&B be presented for Airworthiness Certification.

"Weight and Balance is on the FAA ramp check inspection checklist in chapter 56"

Is this checklist current and if so that doesn't make it regulatory.

Note there is potential for variations in semantics and at least 3 different interpretations of Weight and Balance.

Weight and Balance data provided at certification
Updated current Weight and Balance performed after aircraft alterations and equipment changes
Weight and Balance loading calculations performed by the crew

Please reopen this. The other question contains out of date answers on Weight and Balance.

How do we interpret "Loading Information"

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sort: votes


text:
Can a PPL holder fly family and friends aboard an A380?
Would I be able to fly an A380 with a private pilots license and carry family and friends? I know I can fly the A380 with a PPL.

Which country or regulations are you asking about? If it's FAA/USA, we already have this question, although the same general answer probably applies in most places.

You can - at least as SIC. FAA would allow you to be a PIC of any plane as long as an you passed a checkride with an authorized examiner, even with PPL. However, where I live for example, you cannot do the above in high performance and/or turbine aircrafts or those heavier than a certain weight without ATP license.

Yes. But you will still need instrument rating and ATPL theory as this is multi crew aircraft. The amount of learning will be the same as to get CPL. Maybe fees for the license will be lower but who cares if you buy an A380?

Why instrument and ATPL are necessary? Can't you fly any aircraft (in the US for example) as SIC in VFR conditions after just being type rated?

In the US you do not need an ATP to hold a type rating. Private/Instrument/Multi is all that is required. As a private pilot, you can get a type rating in any jet and then fly it legally after meeting the requirements of 61.64.

@Richard I'm saying the same thing

I don't say that you need ATP but in Europe you will have to pass ATPL exams if you want to get IR with ME to be eligible to get TR. MCC will be also required.

@PIXP Sorry - I saw the SIC in VFR in your comment. A Private Pilot with a type rating could fly IMC as PIC, but he MUST (in the US) have an instrument rating and a multi-engine rating to get a type rating. So I was answering your questions as to why and instrument and ATPL were necessary.

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text:
What does it mean to "firewall" an aircraft engine?
I (think) I understand what a firewall is (at least, in a single engine aircraft where the engine is at the front of the fuselage), but what does it mean "to firewall" an aircraft's engines, as described in this incident report: is it just applying full thrust? What is the connection with the physical firewall?

A firewall is simpy a fire-proof wall.

"To firewall" is a phrase meaning to go to full power. Most aircraft throttle controls provide full power when moved to their furthest forward position - the direction towards the firewall separating the nose mounted engine from the cockpit in aircraft in the past. The phrase is still used, just as we "dial" a telephone even though the telephone dial is no longer used, either. A similar one for automobile driving is "pedal to the metal".

Another automotive expression I've heard is having one's "foot in the carburetor", the humorous imaging being that someone pushed the gas pedal so far their foot followed the linkage all the way to the carburetor.

Foot to the floor will do. Full bore does not get fuller. The floor being a de facto firewall where the pedal hits it in any case.

Likewise, "hammer down" comes from long-haul truck drivers, when they would put the truck on sustained maximum speed while giving their foot a rest by literally laying a sledge hammer on the gas pedal.  The invention of cruise control made the hammer obsolete, but the phrase remains in use.

@MasonWheeler that sounds like a bogus etymology to me - got a reference? Most sources indicate that it's related to the firing hammer of a pistol or rifle.

I've long known it from cars, where firewall means to put your foot (on the gas) to the firewall (the wall between the passenger compartment and the engine.)

It's just an expression. It means to push the throttle as far forward as it will go (all the way to the firewall, if you can), or full power.

Like AC-DC says, push the balls to the wall man. From era before engine control quadrants, ends of the controls were balls. Throttle in full, Mixture full rich, Prop control to flattest pitch for max RPM.

Streetcars typically had controllers that rotated around an axis, there's a stop molded into the top of the control stand, which was made of brass.  Hence, "on the brass" indicated full power.  However, you didn't want to spend any time in a resistor point, you would cruise at full series or full parallel.  So "on the brass" was a normal running point, not near as dramatic as "firewalled".

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text:
What clues would have indicated KAL 902 was off course?
Korean Airlines Flight 902 was shot down by a Soviet fighter in April 1978 after the pilot turned through 150 degrees and entered Russian airspace. The New York Times reported it happened around 8.30 pm Paris time, so this happened during sunset. But if he had kept to the correct course, he should have been flying over the North pole and into the middle of the day.
Given that magnetic compasses are not helpful at this latitude, the aircraft did not have an inertial navigation system, and the Earth's surface (if visible) is presumably similar in both directions, what other clues could the pilot have to his heading?
In other words, for flying at high latitudes in the late 70's, what checks were available to the accuracy of navigation?

More specifically, the plane came down near Sofporog and Google says that sunset would have been at about 8:50pm.

According to the German Wikipedia the 707 has been equipped with LORAN-C and VOR. It most likely also had (at least one)
Gyroscopic Heading Indicator.
Wikipedia does not tell something about this concrete plane but these devices where available since the 1950s and there is no reason why this particular plane should not have them.
So from a technical point of view the crew should have been able to detect the deviation from the planned path, given that they had some training in using all of that equipment, and that not all of them broke altogether during the flight (before the rocket hit).

There's an article in the Washington Post April 30th, 1978, just after the flight crew was released by the Soviets, and 10 days after the shootdown.
Pilot of Korean Jet Downed In Russia Fails to Explain Incident
By Kevin Klose
April 30, 1978
The Captain said almost nothing specific and had an airline official sitting next to him as he ignored most questions, but journalists had earlier spoken to the co pilot and navigator without an airline official present.

The only hard information came from the navigator, Lee Kun Sic. He said the plane was not equipped with a special Inertial Navigation System that provides relatively trouble-free directional aid and is especially important in a circumpolar route such as that taken by Flight 902 when it left Paris April 20 headed for Seoul via a refueling stop in Anchorage, Alaska.
Lee, a veteran of 70 such fligts, said the plane, a Boeing 707, was equipped with gyrocompass system that went awry sometime during the flight. Somewhere in polar airspace, the plane veered east and south over the Soviet Union's heavily defended Kola Peninsula. It was shot down after passing over Murmansk at 35,000 feet. Murmansk is the base for the Soviet Union's intercontinental ballistic missile submarine fleet and center for other major military installations.
Lee said that in reviewing the events of the flight he now realized the gyrocompass system, which needs frequent astronomical observations to maintain its accuracy during polar flight, began steering them wrong while he thought he was somewhere over Greenland.
Lee also said a radio navigation beacon called Loran failed as well. There have been reports that the flight plan filed according to Federal Aviation Administration regulations in Anchorage asserted that the plane had an Inertial Navigation System aboard. The new conference was ended before Lee could be asked about this.

I would also point out that it's reported elsewhere, that Capt Kim had doubts about their heading but proceeded regardless. It's asserted that he disclosed this in his apology to his passengers while they awaited rescue helicopters to find them on the lake they'd landed on.
What I find amazing is that they didn't think to keep trying ATC until they got somebody. On their way West and North, the Sun was visible on their left. When they made that huge turn to the left, the Sun would have been on their right and to the rear.  That should have been enough of a clue that they needed to figure out where they were rather than press on regardless.  During the Cold War to discover you're in the far North heading South East is not something to be passive about. They overflew Svalbard before they reached the USSR.  Svalbard, the northernmost airport in the world would have been a decent place to land when completely lost, instead of stubbornly following their nose and arriving over Murmansk 3400 miles from Anchorage.

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text:
Do they wait until all aircraft have landed before winding up an airline?
This BBC article suggests that any announcement about winding up Thomas Cook will wait until late at night and all its planes are on the ground (I guess they don't fly long haul distances?) before an announcement is made about bankruptcy.
What is the significance of this? Surely no airport would turn away an aircraft that needed to land?
Is it an insurance thing?
How do airlines which never have all their planes on the ground get wound up?

It's not about allowing airplanes to land.  Airport authorities do not control landings, air traffic control does. In any case if an airplane was coming to land and were refused the pilots would eventually declare an emergency due to fuel and land anyway.

Could it be the news could reach crew, and you wouldn’t want people to receive potentially life-changing news while operating an aeroplane?

@CptReynolds The news that it might happen is already out, since a good number of hours ago. I'm not sure uncertainty would be better than knowing, even if the news is bad once it becomes known.

@CptReynolds it'd be more to prevent aircraft from being stolen, diverted by crews to places where the aircraft can't be easily recovered by debtors or lease companies owning them.

It takes months or even years to "wind up" any large business, so the timing concern is only about the announcement.

There may also be some financial aspects (waiting for some specific market place to be closed to avoid insider trading or something related I cannot imagine).


text:
Why do we need to fly at lower altitudes at night to prevent hypoxia?
FAA recommends general aviation aircraft to stay below 5,000 ft at night time.
I thought the reason is that oxygen usage with our eye's rods since the rods uses much oxygen and rods can get hypoxia which makes tunnel vision and eventually not able to see outside.
But one of my friends claimed the reason why we are supposed to fly at a lower altitude to prevent from hypoxia is that at night there is higher pressure near the ground which makes fewer air molecules at high altitude at night than daytime.

Is this true that we get hypoxia more easily at night time because of pressure and that's the reason why FAA recommends us to fly below 5000ft?
If the question number 1 is not true (from my understanding), is rods problem the only reason why FAA recommeds us to fly below 5000ft at night time?

The main reason stated by aviation authorities is due to the impairment of vision, your rods provide the majority of your sight in low light conditions and are affected by the lower oxygen levels. However, your colour perception (provided by your eye's cones) is also affected and this is already degraded at night due to the lower light levels.
The below quote is from an EASA General Aviation Safety Briefing on Preventing Hypoxia

Hypoxia also impairs night vision. Because the rod cells in the eye, which give us night vision, require a lot of oxygen, a lack of oxygen causes visual impairment.

Regarding your friend's point on the diurnal atmospheric changes, this should not be a factor as the suggested altitudes by the aviation authorities on hypoxia prevention should be given as a pressure altitude (i.e. the altitude with the standard altimeter setting of 29.92 inHg or 1013Hpa)
Hope this helps


text:
Is there a minimum start altitude for autorotation landings?
If a helicopter is flying relatively low, say for sightseeing, can it still land using autorotation if required?
What about if there was an issue during a routine landing? Is there any cutoff point where autorotation is no longer feasible?

What you're looking for is the height/velocity curve, some times called the 'dead man's curve'. This shows the altitude and speed requirements for a safe autorotation, plus the height and altitude conditions under which an autorotation is probably not possible.
A lot of variables go into this, and the h/v curve is specific to the particular helicopter, and in particular, whether the helicopter has a high inertia rotor system or low inertia rotor system.
For example, the Robinson R22 has a low inertia rotor system, meaning that the rotor blades are fairly light, and thus don't have a lot of inertia to remain spinning in the case of engine failure. A similar size helicopter, the Enstrom F28, has a high inertia rotor system, so the h/v curve for the Enstrom looks quite different from the Robinson, but is somewhat similar to another popular high inertia helicopter: the Bell 206 JetRanger.
As the article notes, Robinson doesn't recommend a climb out under 45 knots speed, while Enstrom allows it at 17 knots. This limitation is governed by the h/v curve, not performance. While the Robinson could climb out at lower airspeeds, it wouldn't be safe in the event of engine failure.
Disadvantages of a high inertia system are that it uses more fuel, and is slower to accelerate under power in low rotor speed conditions (which are also potentially deadly).

There are different techniques for low altitude autorotations and high altitude autorotations.
If your altitude is low, you most probably have to land directly ahead and you will only have time to lower the pitch, flare, then use the last rotation on pitch to have power, then land the helicopter.
If you have altitude, you can direct the helicopter to where you have decided to land, you can use the airspeed and rpm of the rotor system to reach to your landing area with a safe airspeed for a flare and landing.
As far as I know there is no unfeasible point for a autorotative landing. A safe autorotative landing is completely about the airspeed and altitude which you had the engine failure and your landing area. High altitude autorotative landings may change your flare height.


text:
What was the first aircraft fitted with both an FDR & CVR?
What was the first production aircraft to be fitted with a Flight Data Recorder (FDR) and Cockpit Voice Recorder (CVR) as standard by the manufacturer?

@mins I figured at some point an airliner manufacturer such as Boing would have made a decision similar to the Trans Canada one in ymb1's answer; where they would fit CVRs to all aircraft of a particular model/range as standard. It would seem it was regulation that forced (American) manufacturers to fit them to all aircraft as standard so they would have been fitted to many production aircraft at once.

The problem with manufacturer initiative could be that recorders need maintenance, so providing them, even for free to an airline will cost the airline for the life of the aircraft (or they will need to remove the recorder).


text:
How does a labyrinth seal work when the engine isn't rotating?
I believe I understand how a labyrinth seal in a turbine engine works when a the engine is running.
Any oil that makes it past the first part of the seal is thrown outwards due to the centrifugal force, forms vortices and therefore cannot pass the second part. I know there's a bit more to it, but to me that seems to be the important part (please correct me if I'm wrong).
However I can't understand what stops the oil passing through when the engine stops rotating. Can anyone explain this?

Note that the oil pump is engine driven and the oil pressure quickly drops when the engine spools down. Also, at least in the engines that I am most familiar with, labarynth seals are generally pressurized with bleed air which counters any oil pressure on the other side of the seal.

An example of oil labyrinth seal use
I'm taking the bearing sumps example. There are several bearings to maintain the engine rotors and shafts centered within the core and the stators. Some may use labyrinth seals.

Source.
Pressurized cavity during operation
In a bearing sump with classic dry design, oil is provided directly to the bearing, and labyrinths seals maintain oil within a first cavity (the sump). There is another cavity around the first where compressed air is injected. Air is tapped for internal use from a compressor stage (bleed air).

Source.
This way if oil escapes the first labyrinth of the oil seal, it is contained by the pressure of air coming from the outer cavity on the other side of the seal.
Actually air, which is provided at a higher pressure than oil, will enter the inner oil cavity and mix with oil to form a mist. This is why scavenged oil must then be filtered to separate air when returning to the oil tank (oil must also be cooled has the bearing generates a significant amount of heat).
Oil is directed to the bearing using jet nozzles, the sump is not completely filled. Someone more knowledgeable may explain why, perhaps an oil boundary layer would appear and create unnecessary friction:

Source: Gas Turbines, A Handbook of Air, Land and Sea Applications
In today's engines, oil is circulated using pumps. There are two pumps: One to supply with oil and one to scavenge oil. To ensure oil doesn't accumulate into the sump, the scavenge pump has a higher capacity. Both pumps are driven by the rotation of the engine.
Non operating engine
The pumps are mechanical and driven by one of the engine shafts.
When the engine is not operating, the pumps stop, oil is not supplied any more and it leaves the sump by the scavenge pipe. Bleed air isn't necessary any longer.
When the engine is started, the pumps also start. Oil is therefore injected again into the sump.
The bearing can sustain lack of lubrication for a short time, and there can be an emergency system if oil supply from the tank is interrupted.
Residual leakage
As there will be some limited leakage anyway, oil is extracted by the cavity drain and disposed overboard (or returned to the oil tank).

Do you happen to know (this is slightly OT) if this is essentially the same setup used in a dry-sump automotive engine?

Thanks for the feedback. One of these days I'll get curious enough to actually go look up for myself how a dry-sump lubrication system works in a car. We now return you to your regularly scheduled aviation related answer.


text:
What is the purpose of these round paved pads?
What is the function of these round pads at KMWH, Grant County International Airport, in Moses Lake, WA? They appear to be sized to allow an aircraft to turn around, perhaps under its own power or for aircraft with a more limited turning radius, with tug assistance, but do they also contain tiedowns? Why is the left (western) one midway down a small runway? Any history on when they were constructed and why would be interesting.
Consulting airport taxiway diagrams, these do not appear to be a VOR check area, at least currently. Utilizing shapes like these for parking seems less efficient than the concrete shapes to the southeast (not shown below). I have searched for "round pad" and "cul-de-sac" with no success.

To clarify: These pieces of pavement, including the circular areas at the end, are indeed depicted in light gray on the airport diagram. So they aren't just meant for ground vehicles, which was my first thought.

Compass Rose Pads makes sense, and is consistent with this related question: https://aviation.stackexchange.com/questions/25050/what-is-this-star-shaped-symbol-on-the-tarmac

These are now defunct compass rose pads, originally used to calibrate the compasses used in aircraft. You may notice that there are no compass markings on either of the pads, at least in your picture. If you zoom in on Google Maps you will see the remnants of these marks on at least one of the pads.

The FAA requires compass rose declination to be within half a degree, and surveys are recommended every five years. Most aircraft are now equipped with magnetometers and GPS and no longer need to calibrate using a fixed reference. With the shifting of the magnetic pole some four degrees over the last twenty years, maintaining these is more effort than it is worth.
Here is how they are used.

You can also just use a Master Compass.  I swing the wet compass on my homebuilt using a compass app on my phone as a master compass.


text:
In Polikarpov I-153, Were the gulled wings very important?
Lets look to the I153
It looks like it was made in order to make space for pilot to see its front just like here
But What about in the aerodynamics study ?
Are Gulled wing design very important in order to make wings farther away from each other ?
Also what would happen if it was straight just like  ?

The I-153 was a development of the I-15, of which 671 were built. However:

The upper wing of the I-15 was unpopular with some pilots, as it was felt to restrict visibility, so Polikarpov's design bureau produced a revised version, again powered by the M-25, with a longer span un-gulled upper wing.2 This version, the I-15bis, commenced production in 1937,[7] a total of 2,408 I-15bis' being delivered by the time production finished in 1940.2

So the straight upper wing version was built to improve visibility, and many more units were produced than of the I15.
Structurally and aerodynamically, straight or gulled in this way makes little difference. Structurally, any bend is a weak spot, but the upper wing of biplanes usually had pylons in that position anyway to fix the upper wing to the fuselage. Aerodynamically: the bit missing in between the gull pylons reduces drag a tiny bit - the cross wires have phenominal drag though, and that fat little body also drags a lot of air with it.


text:
Do flights of a specific callsign always depart and arrive at the same airports?
I've been doing some research using flight data, but I'm not particularly versed with aviation. From a quick look, it appears that, say, a flight with callsign SAA203 will always be departing from Johannesburg, South Africa and arrive in JFK Int'l airport.
Is this sort of thing always the case, are callsigns only changed when a flightpath is retired, or can a given callsign correspond to multiple flightpaths?

This would probably be better asked on Travel.SE

I'll give it a try, but that looks more like it's for advice on trips, rather than airline data.

Flight numbers sometimes change for unusual specific reasons (e.g. after an accident)

@fooot In my opinion this is definitely on-topic for this SE, and not subject matter that I would expect Travel.SE to be able to knowledgeably address.

@ymb1 related, but not a duplicate

@JWalters I'm not saying it's off topic, just that it could be asked there as well. I don't see why they wouldn't be able to answer it, this one seems very close: Is a flight number unique for the schedule, origin and destination?

@fooot Yes, that one bears some semblance to this, but is tagged airline. This question is much broader, and should be answered with the expertise of industry specific knowledge. Aviation callsigns, and how an operator chooses to implement and designate them, is not the sort of knowledge that the traveling public is going to have a deep understanding of, with the possible exception of typical airline implementation. I am not even sure that this question would be properly on-topic at Travel.SE.

As Dave has already discussed, some aircraft use their registration number (such as N12345 or G-ABCD or SE-XYZ) to identify themselves. Since any one aircraft will have only one registration number, but can fly any number of routes, it clearly follows that a single call sign can be used over time to identify the same aircraft flying different routes, in the case that the callsign identifies the specific aircraft. This is almost certain to be the case in non-scheduled aviation.
Also, specifically in radio communications, it's common for aircraft registration numbers to be abbreviated when used as call signs. Thus you might end up with 2345, G-CD or S-YZ for the above examples. Worse yet, the aircraft that was S-YZ a few minutes ago might now be S-XYZ because SE-KYZ entered the same airspace using its registration number as its call sign, causing a collision between the abbreviated call signs because both would abbreviate to S-YZ!
However, there's another case, which is perhaps more common in commercial, scheduled aviation. Simply enough: diversions. Aircraft sometimes have to land on an airport other than the intended one, for any of a multitude of reasons, not the least of which being weather conditions at their intended destination. Depending on circumstances, this could be an airport that they fly over or near on their normal route, or it could be an airport quite some distance from their originally planned flightpath.
Changing callsigns due to diversions could potentially cause confusion for air traffic controllers, in a situation where there's already some other situation causing increased workload (if one flight has to divert, it's possible others will have to, too), so doing so would likely increase the risk of mistakes. Since aviation in general is very risk-averse, it makes sense to avoid the unnecessary risk and just keep using the same callsign.
A similar reasoning can be applied also to flight numbers as seen by travellers; nobody wants the jarring experience of boarding Acme Airlines Flight 1234 and disembarking Acme Airlines Flight 9876 at the end of the hop! It's bad enough that you ended up somewhere other than you planned.
Thus we have shown that two major categories of air traffic, namely unscheduled (commercial and non-commercial) and scheduled commercial (which in turn can be passenger, cargo or both), can or do keep using their original call sign even if at least the destination airport changes. Consequently, the answer to the question in the title,

Do flights of a specific callsign always depart and arrive at the same airports?

is clearly no because while the departure airport may be the same for any given callsign, the destination airport can change in-flight without the callsign changing, meaning there is no one-to-one mapping between the two.

You may be confusing callsign (with can be multiple things) and flight code/number as FlightAware may display one or both of these things depending on whats applicable. FlightAware tracks publicly available filed flights at a variety of levels depending on what callsign you search/are looking at the answer may change. For example
American Airlines runs flight AA66 (AAL66) from JFK to BCN and the code AA66 is used to identify that flight (AA67 is the return flight). This code may also be used for a code share. Generally these codes stay fairly consistent unless there is an overlap (see ymb1's) comment for how dupes are handled.
Generally non scheduled commercial and private traffic the flight files with their tail number, for example in the US tail numbers are often 5 (or possibly 4) digits and a preceding N. So N12345 may file for a flight from anywhere to anywhere they want to go. This history log is a good example of a charter plane that seems to fly out of KDYL to lots of places.

No, not necessarily.
In the case of the air carrier that I fly for, our call signs (and flight number) are specific to each aircraft, regardless of route. Each aircraft in our fleet has an assigned numerical designator—typically derived from the aircraft registration (tailnumber)—which is used with our company telephony designator to create a unique call sign for each flight.
Suppose our company used the call sign "Acme" as a telephony designator with a three letter designator of ACM. And suppose that I was assigned a flight in an aircraft with the registration N123AB. In that case, regardless of route, our call sign for that flight would be "Acme 123" with the coded designator of ACM123.
However, that is just one example of how call signs are designated. Many air carriers—especially airlines that fly scheduled routes—do things differently.


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Differenciate- the motion of "Nose-up trim" and "Nose-down trim"
I wanted to understand a part in ‘Take Off” where the study starts to explain “… the airspeed for best rate of Climb.”
I am a little confused about the (how to) of pushing the wheel forward to relieve forward pressure
 (nose down trim) -or- Rotate the trim-wheel back towards you to relieve back pressure (nose up trim).
 Is the motion in opposite of when pushed down, nose up trim and vice versa to that motion?
Hope I am explaining it articulately and its comprehensible.

Some aircraft don't have trim "wheels", for example the Comanche has a handle on the ceiling you turn. Others may have a wheel but most of the time are actuated electrically via a switch on the control yoke. I'm also not sure what study you are referring to. Unfortunately your question is hard to follow so it isn't clear what you are asking.

Thank you, my question should no longer be on hold because I was able to b e answered by the last two responses. Thank you. :
)

There are two pitch inputs* in the cockpit: the yoke and the trim wheel. The effects add up - you can achieve the same pitch up moment by the yoke only, the trim wheel only, or a combination of the two. The pitch up or pitch down motion of the airplane is always the sum of the two.
*That is not a very correct statement, but for now let's put things that way for easier understanding.
The difference between the yoke and the trim wheel is that once you let go of the yoke, it returns to neutral. However the trim wheel stays where it is.
So let's say you want 2 units of "pitch up force" (and let's ignore what the actual unit in physics is, it is just a number) in a certain flying situation. You pull on the yoke until you reach the desired pitch. Great. However if you let go of the yoke, you will loose that pitch up force and the aircraft will start to pitch down. That is not what we want - we want the airplane to hold this pitch attitude, stable, for the next 10 minutes. If we move the trim wheel from the neutral position to 0.5 units up, the desired amount of pulling on the yoke is reduced - we still need to pull back on the yoke, but not as much - we only need 1.5 units of pitch up on the yoke because the other 0.5 units is provided by the trim wheel. This is what "relieve back pressure" is referring to. If you move the trim wheel to 2 units up, you can now completely let go of the yoke, and the aircraft is stable.

Is the motion in opposite of when pushed down, nose up trim and vice
  versa to that motion?

I think you might be confusing the pitch input with the movement of the trim tab on the elevator, assuming that your textbook mentions it. On most general aircrafts, a trim tab is used for pitch trim control. A trim tab is essentially "an elevator of the elevator". The elevator needs to move up for the airplane to pitch up. But the trim tab needs to move down for the airplane to pitch up.
Do not confuse how the trim is achieved aerodynamically, with what you input in the cockpit. The trim tab is just one of many ways to control pitch trim. Airliners, for example, do not have a trim tab. However, the principal of operating the trim wheel is the same. It is just a large aircraft uses a different method to hold a stable pitch attitude.

I read the OP's "opposite motion" as referring to the old joystick gaming misunderstanding of "push the stick up to go down" as opposed to "push the stick forward to tip the plane forward" - not to do with the physical operation of the trim tabs.

Understood where you explained 'pitch up force' Kevin.

But I think the clarification of what the motion I was relating to, is the joystick gaming method of what the commenter [IanF1] said. Which is not what I want to do, I know the cockpit is not a gaming device - but reading it game me the idea of that what the motion might be? Maybe even the book was unclear.

I up voted Kevin's excellent answer. I'm wondering, though, if

I am a little confused about the (how to) of pushing the wheel forward to relieve forward pressure (nose down trim) -or- Rotate the trim-wheel back towards you to relieve back pressure (nose up trim). Is the motion in opposite of when pushed down, nose up trim and vice versa to that motion?

is in reference to the relative motion of the aft edge or top edge of the trim wheel.
Considering the trim wheel as a disk, it is typically mounted vertically such that it's plane of rotation is parallel to the aircraft's longitudinal axis and it's axis of rotation is parallel to the aircraft's lateral axis.

In the image below taken from Wikipedia of a Cessna 172 trim wheel, you see that the disk (to the left of the mic) is recessed such that the only part of it protruding is the aft part with the edge having little bumps.
To trim nose up, you would rotate the wheel such that the movement of the bumps would be downward. To trim nose down, you would rotate the wheel such that the movement of the bumps would be upward.
Putting it another way, if the wheel was recessed in a center console between the pilots seats such that only it's top was showing, to trim nose up, you would rotate the wheel such that the movement of the bumps would be toward the back of the airplane. To trim nose down, the movement of the bumps would be toward the front of the airplane.
My apologies if this has been too pedantic.

Thank you Terry! its understood, via the image portrayed. Reading it and actually seeing it with explaining is very vivid. I am studying the cockpit and flight of a Cessna 152 however I will be actually flying the Cessna 172  (I hope its a smooth transition).


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In BGA or ATR's what are the major causes of ODOR in Cabin or Smoke in Cabin?
In BGA or ATR's what are the major causes of ODOR in Cabin or Smoke in Cabin?
There are some of the maintenance activities that are related to removal of Engines or APU.
Removal reason: Smoke in cabin or Odor in cabin
what do you think could be different reasons around it? and is there any ways we can avoid it that can be thought of or detect Odor in the bleed Duct itself?

Odor in a ball grid array? And BGA parts don't come with an APU. What were you smoking? Or are you talking of odor in the British Glider Association? Well, that comes from a lack of deodorants. Sheesh - what did you expect?

The use of compressed “bleed” air for aircraft ventilation and pressurization systems commenced in military jet aircraft in the late 1940s. However, early commercial jet aircraft, such as the Boeing 707 and Douglas DC-8, initially did not take air from the engine compressor to supply the breathing/ventilation air, but instead they relied on drawing air from outside the aircraft using separate  turbo compressors. The system of utilizing compressor bleed air to supply aircraft breathing air is today used in almost all commercial transport aircraft except for the new Boeing B-787. The B-787 utilizes an electric compressor system which acquires fresh air directly from outside, rather than through the engines. Bleed air (used on most aircraft) is not filtered before it enters the air supply. This air is diverted from the mainstream gas path for several purposes, including cooling, anti-icing and cabin pressurization. A variety of air and oil seals are installed in order to minimize the amount of oil leakage from the gas turbine compressors and into the bleed air supply. However, just about all known seals leak and there is no such thing as a seal that does not leak. Only a very small amount of oil is need to leak through a seal to generate a noticeable cabin odor. And, it will be possible to smell the oil long before high oil consumption is noticed. Light oil contamination, well below permissible leakage levels, is often difficult to identify during inspection procedures and, therefore, could result in the smell of oil in the pressurized cabin when the aircraft is put in service. The only solution to completely preventing contaminated air from entering the cabin on aircraft using engine compressed air for pressurization and ventilation is to completely re-design the aircraft's system. And, that's not going to happen!

is there anyway we could add sensors to the existing duct, that could detect toxic gas etc.. and send signals before smell enters into the cabin. (i know adding sensors again will be too expensive, but do you think it could be a solution? or are any existing sensors in the duct that can be programmed to detect?)


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Why don't single-engine jets suffer severe gyroscopic effects?
I was reading up on World War I fighter aircraft, and saw that rotary piston engines, which powered many of those planes, produced extreme gyroscopic effects due to the large, heavy chunk of metal spinning at several hundred RPM; as a result, single-engine aircraft using these engines had extreme difficulty turning to one side but could make exceptionally sharp and quick turns to the other side.
Why don't modern single-engine fighter jets experience even worse gyroscopic precession than their World War I counterparts, seeing how the compressor/shaft/turbine assembly in a turbojet engine is far heavier than a WWI rotary engine and spins far faster?

Related: https://aviation.stackexchange.com/questions/700/do-turbine-engines-on-multi-engine-aircraft-rotate-in-opposite-directions-to-off and https://aviation.stackexchange.com/questions/31614/do-gyroscopic-forces-from-rotating-engines-significantly-affect-yaw-or-pitch

Well, jet engines do have gyroscopic effects.  It is a major concern in the design of the turbomachinery.  When the plane pitches/yaws, the resulting gyroscopic moment causes the compressor and turbine blades to move closer to the case.  If excessive, this can cause the blades to rub into the case, causing loss of performance.
As to why the plane is not affected by the gyroscopic moment of the engines, let's compare a few numbers.
Take a typical WWI era plane such as the Vickers FB19 powered by a Le Rhone 9J.  The engine has a mass of 146 kg, the majority of which is rotating and produces 110 HP. The plane has a maximum takeoff mass of 675 kg, which includes the engine.  The rotating mass is a fairly sizable fraction (~20%) of the mass of the plane.  Therefore the gyroscopic effect of the engine has a big impact on manueverability.
Now compare that with an F16 powered by an  GE F110 engine.  The high pressure spool of the engine has a mass on the order of 200 kg (the whole engine is about 2000 kg and the high speed rotating spool is about 10% of that... sorry I don't have a specific reference).  The max takeoff mass of the plane is about 19,200 kg.  The rotating mass is only 1% of the total mass of the plane.  So the gyroscopic effect is not so important. i.e. compared to the moment required just to turn the plane itself, the gyroscopic moment is not large.
Further, to be more precise, the gyroscopic moment is not actually proportional to the mass, but to the mass moment of inertia, which is proportional to radius squared.  A lot of the rotating mass of an older rotary engine was at a fairly high radius, whereas a lot of the rotating mass of a jet engine rotor is at a fairly low radius.  Although I have not done the calculations, my guess is that a modern fighter jet engine spool probably has a lower moment of inertia than a WWI rotary engine, despite the higher mass.
Edit:
In response to the comment by J Walters, let me try to make this a little more precise.  The moment required to perform an angular acceleration is $M=I\alpha$, where $I$ is the moment of inertia.  Let's assume that the plane is a rod (length >> width or height).  That's not totally correct, but it's good for an order of magnitude approximation. Then from this formula, $I=(1/12)mL^2$.  So for the FB19, the moment of inertia is $(1/12)(675)(5.54^2)=1726 kg-m^2$.  For the F16, $(1/12)(19200)(15.06^2)=362885 kg-m^2$.  So, comparing these two, the moment that the control surface have to apply to turn the plane (at a given angular acceleration) is 200x higher for the F16.
Now, let's look at the moments due to the gyroscopic effect. The gyroscopic moment is $M=J \Phi \times \Omega$, where $\Phi$ is the angular velocity of the aircraft maneuver and $\Omega$ is the spin angular velocity of the engine, and $J$ is the polar moment of inertia.  I said before that I expected $J$ for the F16 to actually be lower due to lower radius, but let's just assume they are the same.  The Le Rhone spins at 1,350 RPM.  I don't know exactly, but I know the F110 high pressure spool top speed is between 15,000 - 20,000 rpm.  So the gyroscopic moment is about 10 - 15x higher for the F16.
And as Peter Kampf pointed out, the aerodynamic forces go up too. The FB19 had a top speed of about 100 mph whereas the F16 can hit 900 mph at sea level.  From NASA's excellent series, both lift and drag scale with velocity squared.  So the aerodynamic forces are 81x higher for the F16.
So, in summary, yes, the gyroscopic moment is one order of magnitude larger on the F16. But everything else that the plane has to deal with during maneuvers (the moment of inertia of the plane itself, aerodynamic forces), are two orders of magnitude higher.  So the gyroscopic forces are less relevant in comparison.

+1, and add to that the flight speed is much higher, so the aerodynamic forces acting on the jet aircraft are much higher relative to the inertial loads than they were on WW I aircraft. When aerodynamic loads are low, the engine needs to be balanced by counter-rotation of two spools. This was key to making the Harrier controllable in hover.

This answer fails to take into account the angular momentum of a turbine engine. While these may possess a relatively low spool mass, the rotational velocity of is measured in tens-of-thousands of RPM, an order of magnitude above the comparative piston engine. The typical counter rotating spools design is also a significant omission.

The torque produced by piston engines was also an issue for military aircraft in the first and second world wars, particularly when engines were operating at full power, as during take-off when it could result in a tendency for the aircraft to yaw. In twin engined aircraft, designers often countered the problem by having the two engines and propellers turning in opposite directions (counterrotation).

Rotary piston engines have a substantial diameter, and most of the mass (the cylinder heads in particular) is concentrated in the periphery. Hence, the moment of inertia of that rotating mass is quite high, and the gyroscopic effects are also much higher than in the case of a mass with less diameter and no so extreme a mass distribution. That's the case of the rotating compressor and turbine blades. It's true that the angular speed is much higher here, but it's not as important as the distance of the element of mass from the center of rotation, that is squared...

The torque effect doesn't come from the spinning mass of metal, it comes from the propeller biting into the air to produce thrust, producing an opposite and equal reaction as Sir Issac Newton observed... same reason a helicopter needs a tail rotor to counteract the torque of the main rotor, which also works by deflecting air while producing torque in the opposite direction. It's the air resistance to the propeller/rotor that produces the bulk of the torque, not the gyroscopic effect of spinning metal.
All prop planes experience this, although the effect is not nearly as pronounced in a Cessna 152 with 110 hp as it is with a FG1D Corsair or Hawker Tempest with 3000 hp. With larger WW2 fighters, careless application of power could flip the plane over from the sudden application of torque, while any torque effect in a 152 is pretty much unnoticable due to the low power.
There was one WW2 fighter that didn't have this torque effect... the P38, with twin engines and props that rotated in opposite directions, canceling out the torque effect. A common tactic of P38 pilots attacked from the rear was to roll left. Single engine fighters couldn't match it's roll rate in that direction due to the torque effect of their single engine and prop. The P38's poor high altitude performance led to it being sidelined in the European theater, while it was quite popular in the Pacific theater, where the combat tended to occur at much lower altitudes.
The Dornier 335, with it's fore and aft engines, would have also been free of torque effect as the props rotated in opposite directions, only it never made full production and saw only very brief combat use.
Turbines in modern fighters don't produce nearly the torque effect because most of their thrust comes from hot gas being expelled to the rear from the turbine or afterburner which produces little (turbine) to no (afterburner) rotational torque. Most modern fighters have low bypass turbofans for better efficiency, but they still derive the bulk of their thrust from the exhaust, not the front turbine.

The question is specifically about gyroscopic forces, not torque. Maybe you wish to modify your answer?


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Why did the Mercure use cascade-type reversers?
There are three main types of jet-engine thrust reversers:1

Target-type reversers are seen on most civilian turbojets and low-bypass turbofans;2 they have the instantly-recognisable buckets that swing out behind the engine to deflect its exhaust (from both the engine core and - if present - the bypass duct) forwards.
Clamshell-type reversers, seen on some turbofans (both low- and high-bypass) have (as the name suggests) clamshell-style doors that open up from the engine cowling to deflect air forwards.  Clamshell reversers on low-bypass turbofans (“hot” clamshell reversers) generally deflect both the core and bypass air, while those on high-bypass turbofans (“cold” clamshell reversers) usually only bother deflecting the bypass air (which reduces maintenance costs and makes the reverser mechanisms last longer).
With cascade-type reversers, seen on most high-bypass turbofans, the entire rear portion of the cowling slides rearwards, diverting the engine’s bypass air forwards through the resulting gap.

Turbojets and low-bypass turbofans generally3 use target or hot-clamshell reversers, as much of the engine’s thrust (or all of it, for turbojets) comes from the core airflow, and said airflow thus has to be deflected forwards (along with the bypass air, if any) in order to produce net reverse thrust.  In contrast, high-bypass turbofans, the vast majority of whose thrust comes from the bypass air and only a  small portion from the core airflow, can get away with only deflecting the bypass air and leaving the core airflow alone (and thereby saving on maintenance, because jet engine core exhaust is really really hot and filled with delightfully corrosive combustion [by]products); as a result, they mainly use cascade or cold-clamshell reversers.
Enter the Dassault Mercure (an unsuccessful French jetliner from the seventies strongly resembling a longer, shorter-ranged 737-200), which used a pair of low-bypass JT8Ds, and, yet, if this photograph of a landing Air Inter6 Mercure is any indication...

...used cascade reversers.7
I’m having trouble seeing how this would work; for the engines to actually produce reverse thrust, rather than (an albeit diminished net amount of) forward thrust, would seem to require - for the reasons stated above - the use of target or hot-clamshell reversers, which redirect both the core and bypass airflow, rather than cascade or cold-clamshell reversers, which redirect only the bypass airflow.
What am I missing here?  Did Dassault have some magic trick up their britches, were the Mercure’s reversers meant merely to reduce the amount of forward thrust generated (and not to produce actual reverse thrust), or is that picture not what it looks like?8

1: For diagrams of the various types of thrust reversers, see the thrust-reverser tagwiki.
2: Low-bypass turbofans (seen on most narrowbodies designed from 1960 through 1980) have a bypass ratio less than 5:1, and generate the majority of their thrust from the engine core; high-bypass turbofans (seen on all widebodies except for one early Soviet design and on most post-1980 narrowbodies) have a BPR equal to or exceeding 5:1, and get most of their thrust from the bypass air.
3: For obvious reasons, I am ignoring jets that don’t have thrust reversers (such as essentially all fighters, early Caravelles, the BAe 146,4 and the F28).
4: I am aware that the BAe 146 uses high-bypass turbofans; footnote 3 applies to all jets, not just turbojets and low-bypass turbofans, but I couldn’t think of anyplace better to put it.5
5: Hey, I can nest footnotes!
6: The type’s only customer (Dassault sold them nine production Mercures, then refurbished the prototype and sold that to Air Inter as well).
7: (Image originally by Eric Salard at Flickr, via Dura-Ace at Wikimedia Commons; shrunken by me.)
8: Well, it’s definitely a Mercure either landing or rejecting a takeoff (as evidenced by the extended spoilers), but maybe what appear to be cascade reversers aren’t what they seem to be?

I would say most turbofans use clamshell reversers on the fan exhaust, not cascade reversers.  Cascade reversers require translating cowl sections that expose the cascade grille and operate blocker doors to close off the flow behind the cascade.   They tend to be slow acting compared to simple deflector buckets.  The CRJ200's CF34 has mechanically actuated cascade reversers and they are fairly useless, because by the time they are fully deployed you only get a second or two of reverse before you start to stow them.  The later CF34s have fan clamshells and work way better.


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Why do almost all overwing exit slides open over the trailing edge of the wings, and almost none over the leading edge?
Almost all narrowbody jetliners, and many widebodies as well, use overwing exits to augment their evacuation capabilities; to escape the aircraft, a passenger or crewmember in the exit row pops the hatch next to their seat, and then everyone else1 chases them out onto the wing.
At this point, depending on the aircraft, they may simply slide down the flaps to safety, or a slide might inflate if the wings are too high above the ground.  Either way, though, they’ll be going over the trailing edge of the wings if it’s a land evacuation;2 even if the aircraft has multiple overwing exits per side (common among the larger jetliners), or if there’s a tail-mounted engine waiting to gobble up trailing-edge evacuees (like with the Fokker 70), everyone going out on the wings still evacuates off the trailing edge.
I know of only a few airliners with overwing exits that specifically direct evacuees over the leading edge of the wings, and two of these are very special cases:

The Concorde’s wings extend for most of the length of its fuselage, so it would be essentially impossible to fit enough exits in without having some going over the leading edge.
The Il-62 has a set of engines so close behind the wings that even the emergency-exit designers realised it would be a bad idea to send evacuees over the trailing edge (also, its overwing exits don’t have slides - instead, you have to slide down a rope over the leading edge of the wing).
The DC-10/MD-11 family has overwing evacuation slides that go over the leading edge of the wing, as do some A310s, making these, so far as I am aware, the only subsonic airliners without engines right behind the wings to use leading-edge overwing exits.

For low-slung narrowbodies, where you slide down the flaps to get to the ground, the predominance of trailing-edge overwing exits is excusable, as the flaps are on the trailing edge of the wing; however, even for large narrowbodies and widebodies with inflatable overwing evacuation slides, the slides still overwhelmingly open rearwards, over the trailing edge.
Why are overwing exit slides leading off the trailing edge of the wings so much more common than ones that go out over the leading edge?

1: I exaggerate slightly; some of the passengers will likely lock themselves in the lavatories or run up and down the aisle(s) screaming like chickens with their heads cut off, and one or two might even use the exit doors at the front and/or rear of the plane.
2: Ditchings work somewhat differently, and some aircraft do call for occupants to fall off the leading, rather than trailing, edge in this case.

Why would you expect engines to be running during evacuations?  One would think that they either stopped of their own accord or as a consequence of the crash (which might be why you're evacuating :-)), or the pilots would have shut them down.

@jamesqf: Maybe there's something that keeps the engines from being shut down (for instance, if the engine-control cables were severed by a rotor burst in one engine or a break in the fuselage).  Maybe the evacuation was initiated from the cabin and the pilots only find out about it (and start the engine-shutdown process, which takes time) when the exits pop open and illuminate the O/W EXIT lights in the cockpit.

While they likely aren't running, engines are likely to be a high risk for fire location, so I think it's reasonable to raise eyebrows at exit slides that delivery people in their proximity.  At any rate, I think the question is interesting enough to have merit with or without the digression about engine location.

The trailing edge is closer to the ground, so evacuation there is less dangerous.


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Why have converging runways?
This is Ramstein air base in Germany,

Why would you want to have runways converging (or diverging) like that, doesn't seem to do you much good in terms of parallel usage (either the approach, or the go-around would be exciting).
The only reason I can think of is that it gives you more separation when launching aircraft in rapid succession, but then again only in one direction. And it's not like the military would bother much with separation anyway when there's a – shall we say – pressing reason to get in the air fast.

My guess would be that they didn't have any more land at the far end.  :-)

@Lnafziger, hah, good point. Didn't cross my mind.

Could also be a result of a geological survey.  Perhaps the ground wasn't stable enough along the parallel line?

A taxiway (India) was converted to a runway (8-26) in 2004-2005.

It is not just military bases.  Here is the runway diagram for San Juan, Puerto Rico.

Ramstein is a major US logistics airbase in Germany. Originally Ramstein used to have only one runway. The runway was built with fighter aircraft in mind and could also host C-130 Hercules aircraft. Bigger freight aircraft and passenger aircraft could not use Ramstein and were handled at Rhein-Main base, which was at Frankfurt's international airport.
When Frankfurt needed to expand their civil operations, Rhein-Main base was closed and all the US military tranport operations were transfered to Ramstein. In order to accomodate the big transport aircraft at Ramstein, the airport needed an upgrade. To keep the base open during construction works it was elected to convert the old India taxiway into a runway (08-26) which was made longer, wider and thicker that the original 09-27 runway. Also new aprons were added to the North and South of the runways. When the work was completed in 2005, the old runway was closed for reconstruction. It was then resurfaced and extended so that since 2008 there are two operational runways at the airport, so that in case of maintenance or an incident the operations can continue.
There is no relation to launching fighter aircraft in rapid succession.

Are you saying that they don't use both runways at the same time then?

@JayCarr no I am not saying that.

Interesting history, but doesn't seem to answer the OP's question, "Why have converging runways?"

@Ken it answers why the runways are converging that way in this special case. Despite the questions title, OP didn't ask for more.

Diverging departure paths during a surge (remember Ramstein is a military base, and used to have QRA interceptors on standby 24/7) is probably the main reason here.
Shaves a few seconds from the time needed to get all the aircraft in the air in an emergency.
Landing them all rapidly is less important, as most would be expected to not make it home, such is the nature of military planning for all out war.

As you can see, the alert pads are at the end from which the runways diverge (the far end in your photo), at the other end there's no quick way to enter the runways at all (you need to backtrack along one to reach the treshold of the other). As these would have been constructed with the prevailing winds in mind, that's no real problem.


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How do I choose the correct airfoil?
I am currently working on a personal single seat, piston aircraft that I would fly myself and I am currently in a bit of conundrum when it comes to my wing design. In this project, I assigned us in 2 basic groups. The guys that work on the chassis and the guy (me) that works on the aerodynamic surfaces. Namely wing, surface controls, tail and such. It is a standard pull configuration aircraft, tricycle landing gear. My problem here is that I am kind of undecided when it comes to my airfoil of choice, so I thought of giving the forum a go and see if anyone can illuminate or inspire me.
As of now, http://airfoiltools.com/airfoil/details?airfoil=naca643618-il has been my choice, but maybe I am starting to think that other options could be better so let me write here a few specifications that could come in handy regarding the aircraft.
The main body will be build of steel tubing covered either in Aluminium or fabric. This will be the final choice once we calculate how much lift we can actually produce.
The wings and other surfaces will be made out of carbon fiber. I will be the one mainly working on this, and they will be attached to long solid cuboids spanning from one tip of the first wing, through the body and all the way to the tip of the second wing. The shape and dimensions of these cuboids will be determined through a FEA after we have the correct wing profile (so we can play with the variables afterwards or maybe even find better solutions). The wings will either be attached with rivets to the cuboid or with standard well shaped bolts. TBD.
The aircraft is planned to be mostly used at not so great speeds. If we can achieve a takeoff at 16-20 m/s with flaps on it would be fantastic. I would not like the top speed to be anything great either. I mostly would use this in very good still weather to cruise around the fields.
I can afford having an airfoil that is a bit thick, but would like to manage the turbulence that would be created by boundary layer separation in high thickness and/or camber foils. Maybe I will modify a bit my final selection.
The wing will have flaps, in fact it will be a flap that extends at around 35% of the total span of the wing. It will be a modification of the slot and Fowler flap (a sort of optimized approach that mixes both) whose final geometry will of course be dependent on airfoil selection.
P.S : I use Fusion 360 for modeling, Autodesk CFD to calculate the total lift of the full 3D modeled wing/aircraft.

Welcome to the site @Deathcoder, you certainly have an interesting project. Unfortunately your question is extremely broad, and also open to opinion and therefore not a good fit for the site. This isn't actually a forum, but a Q&A site which requires a bit more of a focussed question. If you could narrow this down to fewer dimensions or put some limits in it we may be able to answer.

Terms fist, to avoid any misunderstandings:
What you call cuboids is normally called a wing spar. It consists of spar caps for the tension and compression loads and a web between the caps to transmit shear. And yes, it runs all the way from one wingtip to the other.
The spar carries the bending moment which has its maximum at the center and is zero at the tips (unless you use winglets). The more distance there is between the two spar caps, the lighter the spar can be built, so a thick mid-wing airfoil helps. Your choice of the NACA 64₃618 is a good start. I would advise, however, to taper the wing to something like a NACA 63₃412 at the tip. Thinner airfoils have lower minimum drag and higher maximum lift coefficients which helps to avoid the tip stalling first.
Or you move to newer airfoils which have been optimised for longer laminar boundary layer runs. Since you plan to use carbon/epoxy for the wings, you might take advantage of the exceptionally smooth surface this makes possible. The NASA contribution is of course the NLF series, NLF standing for natural laminar flow. The NLF(1)-0416 or the NLF(1)-0215 would be possible candidates. Even better designs might be possible when you search for modern glider airfoils; however, the published ones generally are at least 30 years old. Glider airfoils are optimised for minimum Reynolds numbers of around 1 million; when used in a GA aircraft this might be a bit conservative but could fit well to your low speed requirements.
The ultimate step could be to design your own airfoil. Take my glider recommendation and use XFOIL to tweak it to what you really need.
One last word on your choice of flaps:
When the inboard span uses powerful slotted flaps, their increased circulation will change airflow at the outer wing in such a way that the outer wing will stall before the inner wing had a chance to demonstrate it's lift potential. Either stay with plain flaps (for which the HQ-17 was designed - make sure you calculate it with a positive flap deflection at slow and negative at fast flight speed!) or add slats to the outer wing. In order to keep complexity manageable, I would recommend to use plain flaps and flaperons over the full span.

Thank you for the answer. I have previously thought of simple flaps but a slotted design increased the center wing area design so much and offered a very good amount of lift ( anallytically from my cfd models ). They did however stall and increase the drag quite a lot at take off so to reattach the flow i added vortex generators on the Underwing opening that reveals the flap. I cannot explain it well but it was a very interesting gemotery. I will upload here a 3d model  soon

I've written an add-in for Fusion360 which will probably help you: it collects your proposed operating conditions, then inserts for you the best airfoil shape that it knows, out of a library of 768 base foils each of which has been optimised through thousands of hours of CPU time using particle swarms.
You can read a bit more about the history in my autodesk forum post here: https://forums.autodesk.com/t5/fusion-360-api-and-scripts/add-in-announcement-hydrofoil-and-airfoil-tools-seeking-your/m-p/9453985/highlight/false
Here's the add-in page:
https://apps.autodesk.com/FUSION/en/Detail/Index?id=5447707798035545266&appLang=en&os=Win64
p.s. NACA shapes are never the right answer - that idea pre-dates computers, and if you read their latest application notes, they tell you not to use their shapes because modern computational methods are always superior.  By way of example - I analyzed all 9999 series 4digit NACA foils, and several thousand 5 digit ones (200CPU cores took 3 months), then selected the best-performing CL/CD for each of the following Reynolds numbers.  The margin by which CFD-optimised shapes outperform the BEST possible NACA shapes is the second column.
Re          CFD outperformance
300.00              146%
400.00              155%
500.00              148%
750.00              146%
1,000.00            150%
1,250.00            178%
1,500.00            182%
2,000.00            175%
2,500.00            172%
3,000.00            172%
3,500.00            175%
4,500.00            180%
5,500.00            111%
7,000.00            150%
8,192.00            136%
10,000.00           139%
12,500.00           148%
15,000.00           145%
20,000.00           145%
25,000.00           147%
30,000.00           142%
35,000.00           139%
45,000.00           136%
55,000.00           133%
65,536.00           129%
80,000.00           125%
100,000.00          131%
125,000.00          139%
150,000.00          143%
200,000.00          150%
275,000.00          155%
350,000.00          153%
400,000.00          149%
500,000.00          152%
620,000.00          158%
750,000.00          169%
1,000,000.00        184%
1,400,000.00        208%
1,700,000.00        225%
2,000,000.00        224%
2,500,000.00        203%
3,000,000.00        179%
4,000,000.00        184%
5,000,000.00        178%
6,000,000.00        174%
7,000,000.00        160%
8,192,000.00        142%
10,000,000.00       142%
13,000,000.00       132%
16,000,000.00       114%
20,000,000.00       134%
25,000,000.00       123%
30,000,000.00       133%
36,000,000.00       201%
45,000,000.00       127%
65,536,000.00       249%
81,920,000.00       154%
100,000,000.00      131%

200% means that the CFD-optimised shape Cl/Cd is double the NACA Cl/Cd

A few of the obvious factors to consider in choosing an airfoil include:

intended speed range
presumed pilot's skill level
intended maximum weight
size of aircraft
Your skill in fabrication

From the intended maximum weight and intended speed range, you can get some idea of the wing loading you want. Given your intended (relatively low) minimum takeoff speed, you need fairly low wing loading.
With some idea of the wing area, you can start to think about how to achieve that: greater wing span vs. greater chord. As a simple guideline, something that has a really "clean", low-drag design will tend to benefit from a high-aspect ratio planform. Conversely, a higher-drag design will work better with a lower aspect ratio of wing. To give a couple of extreme examples, competition sail planes often have an aspect ratio around 50:1. A piper cub had an aspect ratio of 7:1, and hang gliders are often around 1:1.
With the chord and operating speed chosen, we can compute the range of Reynolds numbers we care about.
With that, we can also start to think about pilot skill level. For example, let's consider the NACA airfoil you suggested. With a minimum of 20 m/s and a 0.1 meter chord, we'd get a Reynolds number around 50K. Looking at the Cl vs. alpha curve for this airfoil at 50K:

For the moment, the part we care most about is the right side of the curve. Note how it curves upward, then has a very sharp peak and drops again very quickly.
That's telling us that (at this Reynolds number) the airfoil has a really nasty stall--as we move to higher angles of attack, it produces more lift--then with just slightly greater angle of attack, it stalls and the lift drops like a rock. In this range of Reynolds numbers, this could be pretty tricky to fly, even for quite an experienced pilot.
By contrast, if you can be reasonably certain your Reynolds number will be at least a million, the picture changes quite a bit:

In this case, the stall is much more gentle--in fact, the lift isn't dropping at all. We have to look at a separate plot to see that while the lift isn't dropping, the drag is rising sharply, so our L/D ratio (and with it, our glide path) drops very quickly:

Based on these, we can guess that this airfoil was probably really designed for higher Reynolds numbers. At 50K it's basically evil. At 1M it's more manageable, but still kind of a handful--especially since, with such high drag, when you stall your air speed (and with it the Reynolds number) will start to drop very quickly, so unless you react to recover from the stall quickly, you're going to drop into the range where you're going to lose lift as well.
Let's give a little thought to that final factor: fabrication skill. Here what we're most interested in is the accuracy with which you're likely to build the airfoil. Some airfoils are really picky about following their profile precisely to get good results. For example, quite a few of Selig's designs have a subtle "bubble ramp" along the upper surface. If you get this even a little wrong, you can end up with quite a bit higher drag than intended.
Other airfoils have quite a bit higher tolerance, so minor deviations from the intended profile won't affect their performance nearly as much. If you aren't very experienced, one of these may be a better choice.

The 50K Re number is way too low. Besides, the lift curve shows laminar separation bubbles which should be treated with boundary layer tripping. In XFOIL, simply set the transition accordingly and the nasty stall behavior is cured.

@PeterKämpf: It's way too low if he's talking about a full-sized aircraft. At least to me, the question didn't make the size entirely clear, and the only estimate of speed was the 20 m/s take off. Could easily be something like a 3 meter drone, in which case 50K really is possible. And yes, a trip strip would probably do a fair amount to tame the stalling. Point wasn't nearly so much the details of this airfoil, as answering the actual question: what factors do you consider, and what do you look for in the plots to find an airfoil that matches your needs.

Using XFOIL to predict stall behavior is asking quite a lot of this piece of software.

I am of the idea that @Peter Kämpf posted, and would have liked to have a modification of my own to the http://airfoiltools.com/airfoil/details?airfoil=nlf0215f-il  NASA NFL-(1)-0215 airfoil that he recommended. I saw it to be a good idea to Put a larger airfoil section on the base and taper it to a smaller verion of itself (and in fact the only problem i have with this is the tail at the end of the airfoil could get too small if i tended to go for a delta win formation, so that is out of question. A delta wing would be too hard to material-engineer the end of the wing. ) so the best i thought of was it to taper it not so much, and increase the wing area at the base a bit. Would have been interesting as it would have made for a stronger structure to hold my weight, id like to keep stuff light.
The problem i have with the airfoild with an xfoil calculation is that, i pretty much made a Aoa-Cl-Cd table for angles, but xofil predicted the sepparation zone being a bit lowere in the airfoil at higher Aoa's * but not much * , 10 DEGREES.
The Simulation is made in CFD at a decent mesh size at quite a few iterations.

Is the xfoil table, for engineering purposes, accurate to a degree?
Also i thought of making a small modification to the airfoil, and add a bitsy more camber at the 60-65% of the camber line length. And see if i can stall the sepparation with 3 decently sized vortex generators. Also ill do some flaps simulations aswell.

Make sure you calibrate your CFD code before you believe anything that is produced by it. That is, get wind tunnel data and replicate the wind tunnel conditions in a model. Make sure you know what tunnel corrections had been applied - it is best to use raw results. XFOIL has been tested a lot already and is a bit optimistic on the lift after separation starts. Turbulent flow is still not modelled correctly by any software, regardless how expensive it or the computer it runs on is.


text:
Why there are nearly no upper wing jetliners?
Whenever I look at the western airliners. All of their wings are always mounted on the lower part of the fuselage except the Dash 8 series which have turbo props.
But the Soviet jetliners have their wings on the top of their fuselage like the Antonov AN-158
My guess is they are mounted on the bottom because it makes reaching the engines possible and even the Soviet planes are designed to be few meters above the ground to make it easier to access the engines just like the western Dash 8 planes [maybe it's a coincidence because they don't make big airliners and dash 8 planes are small]
Is there an reason why nearly all jetliners have bottom mounted wings?

Don't forget the Avro RJ-85 / RJ-100

Dash 6, ATR 42/72, Short Skyvan/330/360, CASA C-212/235/295, Let L-410, Lockheed L-100...

I suspect the Russian planes, like military jet transports, have their engines mounted high to help protect them from ingesting dirt &c when they land on unimproved strips.  That's seldom a consideration for western commercial airliners.

@jamesqf -- yeah, the Tupolev Tu-204/214 are the only low-wing Russian jetliners I can think of with wing-mounted engines


text:
How do pilots protect their necks in jet fighters?
My uncle once told a story of a pilot forgetting to strap his neck, which snapped mid-flight and the plane crashed. How do pilots strap their neck properly?

Your neck won't "snap off", most flight suits don't have neck support so I'm not sure what you are referring to.

@RonBeyer I am just saying things my "Brother of my mother" told me thats it

This may not have an application to reality, that's what I'm saying... I've never heard of internal decapitation in fighter pilots, flight suit or not.

Consider the possibility that "brother of your mother" (uncle, in English) either 1) doesn't know what he's talking about; or 2) is telling you "tall tales" for some reason.

@RonBeyer so why would an fighter jet (tag) pilot would die mid-flight other than heart attack etc ?

Blacking out would do it, and has done it. Modern flight suits are fitted to the pilot, as long as they are on, they are "tightened up". The air pressure system does the rest.

They don't need to, because the neck is great at handling vertically upward G force which is the only direction of high G on a fighter. It's not like race cars you have a lot of lateral and front/back Gs that can indeed break the neck.

I think the way they protect their neck is by shooting down the other guy first - just a thought.


text:
Why is the DC-9-80 ("MD-80") prohibited from taking off with a flap setting between 13 and 15 degrees?
A bit of digging into the 7Z9363 accident investigation has brought up some interesting information regarding the DC-9-80 ("MD-80")'s flap system:

Flaps may be positioned in any of the six permanent detents in a 0 to 40-degree range by movement of the Flap/Slat Handle. The authorized flap settings for takeoff in the MD-83 were 4, 6, 11, 15, 17, 20, and 24.73 A “Flap T.O. Sel Wheel” on the center pedestal would allow the pilot to further position the flaps from the position selected by the Flap/Slat Handle position anywhere in the 0- to 13- and 15- to 24-degree range.74 This was used to set the final takeoff flap setting, as determined
by the runway analysis review for the airport/runway.
[...]

[...]
74The Ameristar Air Cargo MD-83 COM, Limitations, page 1-24, stated “Flaps (AFM): Do not use flap settings between 13 and 15 degrees.” [Operations Group Chairman's Factual Report, NTSB docket DCA17FA076, page 32, my emphasis.]

and

4.1.3.1 Flaps
4.1.3.1.1 System Description
The aircraft has an inboard and an outboard flap on each wing. The flaps are mechanically controlled and hydraulically actuated. The crew moves the flap lever to the appropriate detent depending on the flight condition (i.e. take-off, landing). The flap lever has fixed detents at UP, 0, 11, 15, 28, and 40. The lever can also be positioned in one-degree increments for takeoff settings using the Dial-A-Flap from 0 to 24, except for a small do-not-use range at 14. Through a series of cables and pulleys, control valves are exercised and provide hydraulic pressure to the flap actuators to extend or retract the flaps. [Systems Group Chairman's Factual Report, NTSB docket DCA17FA076, page 59, section headings bolded in original, other emphasis mine.]

Reinforcing this prohibition, the DC-9-80's takeoff-flap selector wheel has a yellow "DO NOT USE" label covering the space between the 13-degree and 15-degree markings:

(Image originally by the National Transportation Safety Board [it's on page 32];1 cropped and red-ovalled by me.)
Why does the DC-9-80's flap system come with a prohibition against using flap settings between 13 and 15 degrees for takeoff?

1: The underlying photograph was taken by NTSB personnel, and the red arrow was added by the NTSB to point out the selector wheel in question.


text:
How is the 737 NG/MAX able to operate at a pressure differential greater than that at which the cabin-pressure relief valve operates?
So I was reading about the 737's cabin-pressurization system, and then I came across these two bits of information:

Limitations
Max differential pressure:

Series
Max Diff

1/200's [sic]
7.5psi

200Adv's [sic]
7.8psi

Classics
8.65psi

NG & Max
9.1psi

[...]
Pressure (Safety) Relief Valves
These two valves, located above and below the main outflow valve, protect the aircraft structure against overpressure if the pressurisation control system fails. they are set at Originals 8.5psi, Classics: 8.65psi , NG & Max: 8.95psi.

According to these figures, the 737 NG and MAX have a maximum allowable pressure differential that exceeds (by 0.15 PSIg) that at which the cabin-pressure relief valve opens and vents the cabin pressure overboard.
Given that the purpose of the cabin-pressure relief valve is to prevent overpressure-induced structural damage, and that its activation threshold is presumably set where it is in order to give the necessary margin of safety between the point at which the valve opens and that at which the aircraft's structure would begin to suffer actual damage, allowing the cabin to be pressurized beyond the relief valve's activation threshold seems like it would inevitably come with an erosion of this safety margin and an increased risk of (potentially-serious) structural damage.  (Not to mention how one would pressurize the plane beyond this point in the first place, what with the open relief valve venting the cabin pressure overboard.)
I'm assuming there's something I'm missing here, but what?

That second quote which states that "outflow valves on NG and MAX operate at 8.95 PSI" is incorrect. According to the Boeing 737 FCOM (page 751):

Two pressure relief valves provide safety pressure relief by limiting the differential pressure to a maximum of 9.1 psi.

Accordingly, that "limitation" table appears to be for the pressure at which the outflow valves operate and not the operational limit. Regarding the operational limit, according to the link you shared:

At cruise altitudes above FL370, the max differential is 8.35 PSI. which will result in a cabin altitude of 8000’ at FL410.